It is known in the art to use coated articles in the context of window units such as insulating glass (IG) window units. For example, see U.S. Pat. No. 6,632,491 to Thomsen, the disclosure of which is hereby incorporated herein by reference. In the '491 patent for example, a solar management coating (e.g., low-E coating) is provided on the inner surface of one of the glass substrates of an IG window unit so as to protect a building interior against infrared (IR) radiation and the heat generated thereby. Coated glass substrates of IG units often have to be heat treated (e.g., tempered), prior to IG unit assembly for example, to meet certain code requirements.
Large pieces of glass (whether heat treated or not) may have certain size-related problems related to handling. Large sheets of glass, for example, may be placed through operations relating to cutting, seaming, and/or edge deletion. In one or more of these operations, the surface of the glass may benefit from protection.
Following heat treatment (e.g., thermal tempering and/or heat bending), the heat treated coated glass substrate is often subjected to shipping, unloading, storage on a pallet or the like, robotic handling and/or human handling. One or more of these often tends to damage the heat treated coated glass substrate (e.g., via scratching, corrosion, and/or the like) before it can be coupled to another substrate to form an IG window unit, laminated window, or the like. Yields are reduced due to such damage which often occurs between heat treatment and coupling to another substrate.
For example, coated sheets are often scratched due to (a) rubbing up against other sheets or the like during shipment, unloading and/or storage; (b) pliers used by glass handlers; (c) abrasion caused by gloves worn by glass handlers; and/or (d) other types of rubbing/abrasion. Additionally, corrosion can be a significant cause of damage and is often caused by high humidity conditions, acid rain, and/or other materials which tend to collect on the coated articles during transport, storage and/or handling.
In view of the above, it can be seen that there exists a need in the art to better protect heat treated coated glass sheets in the processing stages following heat treatment and before coupling to another substrate. In particular, increased protection against mechanical abrasion and environmental damage is needed. Over the years, numerous attempts have been made in this regard.
The dusting of coated sheets with Lucor powder separator is often carried out in an attempt to better protect coated glass sheets in processing stages prior to heat treatment. Unfortunately, Lucor powder provides no protection against corrosion damage, and also is not particularly effective in protecting against scratch damage due to the use of pliers, brushes, gloves and the like.
Encapsulating of racks during shipment has also been tried. However, encapsulating racks is labor intensive and has proven only partially effective during shipment.
U.S. Pat. No. 6,682,773 to Medwick discloses a technique where a water-soluble temporary protective layer is applied to a coated glass sheet via a liquid solution. In particular, the protective layer is formed from an aqueous coating composition containing a polyvinyl alcohol polymer which is then dried and may thereafter be removed by washing in water. The technique of the '773 patent may be undesirable in that: (a) the coating is applied in liquid form and thus has to be dried using a sophisticated heat drying process which takes up valuable time and space; (b) the coating is typically water soluble and is removed by washing thereby leaving the coated sheet exposed to potential damage upon contact with water; and/or (c) the protective coating may have the tendency to absorb moisture in hot and/or humid conditions which may result in adhesive bonding to the protected glass. Thus, it can be seen that the technique of the '773 patent may be undesirable.
U.S. Pat. No. 4,710,426 to Stephens discloses a protective polymeric layer on a coated sheet. However, the isocyanate used in the '426 system prevents the protective polymeric layer from being practically removed in a reasonable manner.
EP 1 380 426 also discloses a temporary protective coating on a coated article. However, like the '773 patent, the protective coating of EP 1 380 426 burns off during heat treatment and thus provides no protection during the period after heat treatment when the coated article is subjected to damage/corrosion.
U.S. Patent App. Pub. No. 2006/0065350 to Richardson discloses a protective layer including polyethylene and an optional adhesive layer including acrylic. But these protective layers are limited in size and may not be applied on large sheets of glass, e.g., sheets larger than 100 inches.
Temporary protective coatings described in prior art are typically formed from solutions or dispersions of polymeric materials formed from polymeric materials or waxes. Whereas laminated protective films are removed by hand peeling, different removal techniques to remove temporary coatings may also include the use of organic solvents, water, steam, alkaline inorganic solvents, etc., and thermal decomposition by combustion at furnace temperatures.
Protective coatings formed from liquid precursors may be removed by hand peeling. But application of temporary coatings from liquid precursors may require a longer processing time and/or use of high temperatures to speed up film formation. Thus there exists a need for temporary coating materials which could be cost effectively applied and removed easily on demand by hand peeling process.
In view of the above, it can be seen that there exists a need in the art to better protect coated glass sheets in the processing stages following heat treatment (e.g., thermal tempering and/or heat bending), in particular between heat treatment and coupling of the coated article to another substrate. The protective layer(s) can be easily removed in a processing step prior to coupling the heat treated coated substrate to another substrate. In particular, increased protection against mechanical abrasion and environmental damage is needed between heat treatment and coupling to another substrate in order to improve yields and reduce the likelihood of damage.